What Is the Temperature of a Blue Flame?

The temperature of a blue flame depends on what is on fire. A burning chemical or metal may display a blue color only after reaching a particular temperature, but that threshold can vary.

When a compound burns, its molecules absorb thermal energy, becoming excited and unstable. To move to a more stable state, they emit energy in the form of light. The wavelength, and therefore color, of the emitted light depends on the amount of energy absorbed and expended. The blue end of the spectrum corresponds to shorter wavelengths and higher energy, while the red end has longer wavelengths and lower energy. As temperature is a measure of thermal energy, a compound burning with a blue color should be hotter than the same one burning red.